Nowadays the governmental environment protection agencies demand combustibles with a low level of contaminants, such as sulfur, nitrogen, and metals like nickel, vanadium, among others. On the other hand, it has become necessary to process heavier loads to get the most out of the petroleum however the content of contaminants is increased in the processed oil. Thus, it is necessary the development of new processes and catalytic materials that remove the contaminants from the petroleum hydrocarbon fractions, and thus to reduce the contaminant gas emissions to the atmosphere and in this way to comply with the environmental regulations which are becoming increasingly more strict.
The most efficient processes for the removal of contaminants from the petroleum hydrocarbon fractions are the hydrotreatment processes, which are applied to almost all the petroleum fractions, such as gasolines, diesel, feedstocks for fluid catalytic cracking (FCC) and intermediate distillates.
In the process of hydroprocessing, the light and the intermediate petroleum fractions are hydrotreated and/or hydrocracked in the presence of hydrogen. The hydroprocessing processes encompass all the processes in which a petroleum fraction reacts with hydrogen at high temperature and pressure and they include reactions like hydrogenation, hydrodesulphurization, hydrodenitrogenation, hydrometallation, hydrodearomatization, hydroisomerization, hydrocracking, etc.
Such processes use mainly catalytic formulations specific for the removal of sulfur and nitrogen compounds. The molybdenum-alumina catalysts promoted with cobalt are generally used when the limiting specification concerns only the desulphurization, while the molybdenum-alumina catalysts promoted with nickel are largely used when in addition to the desulphurization it is necessary to hydrodenitrogenate and to partially saturate the aromatics content (hydrodearomatization) in the fraction that requires to be hydroprocessed, this is due to the high hydrogenating catalytic activity of nickel. The procedures for the preparation of hydroprocessing catalysts have been presented in U.S. Pat. Nos. 5,089,462 and 2,853,257, and in the European patents EP 0,448,117 and 0,469,675.
However, spite of all the efforts made to improve the performance of the hydroprocessing catalysts they produce fractions, for example of diesel and/or straight run gas oil (SRGO), which still have around 500 to 600 ppm of sulfur and nitrogen compounds. Because of this, considerable efforts are being made to find more efficient catalysts capable of reducing the content of these contaminants below 10 ppm in the motorcar combustibles to comply with the environmental regulations, which will take effect globally starting on 2006. The applicants of the present invention have discovered that the solution to this problem is to use a nanostructured material together with a procedure for the selective and efficient adsorption of the polar compounds, such as nitrogen and sulfur, from the petroleum hydrocarbon fractions, and thus obtain levels below 50 ppm of the mentioned contaminants.
The performance of the catalysts in the catalytic processes of hydrotreatment and fluid catalytic cracking (FCC) is affected or inhibited by the content of nitrogen compounds in the feedstocks. The removal of the polar nitrogen compounds, by selective adsorption processes (U.S. Pat. Nos. 6,248,230B1 and 6,551,501B1), from the feedstocks (naphtha and diesels) allows a better performance of the catalysts, an as a consequence, for example, the catalytic desulphurization process yields levels between 5 and 50 ppm of sulfur in the combustibles which makes them more active and efficient. The removal of the polar nitrogen compounds allows a good performance, less deactivation, of the catalysts in the hydrotreatment and fluid catalytic cracking (FCC) processes (Engelhard's FCC Knowledge Data Base, html).
Another strategy to produce ultra clean combustibles with ultra low content of nitrogen and sulfur, is to apply selective polar compounds adsorption processes directly to the gasolines, diesel, kerosenes, and other fuels used in the cars, trucks, planes, jets, etc at the end of the producing process or in the gasoline pool (U.S. Published application No. 2002/0043483).
The adsorbent materials for the adsorption of polar compounds of nitrogen and sulfur used in selective adsorption processes are liquid or solid and they are the same adsorbent materials used in the chromatography. However, the adsorbent capability of these materials is limited and a large quantity of them is required to get low levels of contaminants. This involves a large equipment installation, large space and high investment costs. Because of this it is necessary the development of new adsorbents to low the level of contaminants in both the feedstocks for hydrotreatment and FCC processes, and in the liquid combustibles at the exit of these processes. The following patents describe the state of the techniques which are closely related to materials used as adsorbents and their application process.
To be able to yield low levels of nitrogen and sulfur compounds in liquid combustibles, U.S. Pat. No. 6,248,230 B1 proposes a previous stage of removal of nitrogen compounds, by a selective adsorption process, from the feed loads for hydrotreatment process. As adsorbent material it is proposed a silica-gel, an alumina, and an ion exchange resin. The maximum level of adsorption obtained is of around 70% using a light fraction of straight run gas oil (SRGO) with 226 ppm in total nitrogen. The removal of the nitrogen compounds increases the efficiency of the catalytic processes of hydrodesulphurization, which lowers the sulfur levels to 50 ppm without increasing the severity of the reaction conditions.
U.S. Pat. No. 5,730,860 discloses a process for the desulfurization of liquid combustibles and feedstocks of hydrocarbons which contain unacceptable levels of nitrogen, sulfur, and oxygen contaminats, which are denominated as compounds with heteroatoms by the authors. The process consists in placing into contact very small particles of an adsorbent in a fluidized bed with the load to be treated. The adsorbent is saturated by the present polar compounds in the load, which contain nitrogen, sulfur, and oxygen. Then the fluidized bed is transported to a regeneration zone, where it is placed in contact with a flow of light hydrocarbons C1-C4 and H2 at high temperature, to remove all the adsorbed polar compounds, and finally it is transported to an adsorption zone where the cycle is started again. This is a continuous adsorption process in a mobile bed.
U.S. Pat. No. 6,551,501 B1 describes a combined process to increase the efficiency of the hydrotreatment process and thus to comply with the environmental regulations of ultra-low sulfur content with the existing catalysts. The process consists in the selective adsorption of the polar nitrogen compounds from the load to be hydrotreated using solids and liquids as adsorbents. Among the liquids proposed as adsorbents it is found: dimethyl formamide, methanol, n-propanol, and iso-propanol in different concentrations with water and also with sodium hydroxide. Among the proposed solids as adsobers it is found: alumina, silica, silica-alumina, magnesium carbonate, magnesium hydroxide, calcium hydroxide, zinc hydroxide, zirconium hydroxide, AMB-A27, etc. The achieved efficiency in the removal of nitrogen compounds is between 10 and 70% depending on the material used.
The U.S. Published application No. 2003/0163013 refers to selective adsorbent materials for the adsorption of sulfur compounds for the purification in general of any hydrocarbon fraction. The proposed adsorbents are a “Y” zeolite of high specific area exchanged with Cu, Ag, and Na with the oxidation state of 1+, which can adsorb thiophenic, benzothiophenic, and thiophenic dibenzo alkyl compounds with high yield.
The U.S. Published application No.2002/0043484 discloses selective adsorbent materials for the adsorption of sulfur compounds in combustibles (gasolines and diesel). The adsorbents are zinc titanates impregnated with metals such as cobalt, molybdenum, nickel, iron, manganese, copper, tungsten, silver, strontium, vanadium, or mixes of them, in a partially reduced state. The process is carried out at a temperature between 316 and 371° C. in a partially oxidant atmosphere. A high capability of removal of sulfur compounds is achieved, however the amount of hydrotreated hydrocarbon per weight unit of adsorbent is very low, which indicates that the adsorption capability to adsorb the polar compounds by these adsorbents is very low.
All the adsorbent materials that are mentioned, in the aforementioned patents, can adsorb nitrogen or sulfur compounds present in hydrocarbons.